HPRC's Answer

1. There is no “magic number” that is prescribed for “critical decision-making,” due to the many confounding factors—including variations in tasks and individual needs—and research on the impact of sleep restriction (rather than total sleep deprivation) on cognitive performance is limited. But one point is clear: cognitive performance suffers when sleep is reduced even by modest amounts (one or two hours). Sleep restriction (that is, four to six hours of sleep) has cumulative effects on cognition, especially executive functioning, after just one sleep-restricted episode; and reducing sleep modestly (less than seven hours) on a regular basis can degrade cognitive performance comparable to one to three days of total sleep deprivation (no sleep at all). Other studies have reported a decline in cognitive performance that becomes stabilized, albeit still degraded, between days two through six on a restricted sleep schedule of four to six hours. You must remember that a “sleep debt” will occur from a single episode of sleep deprivation, resulting in subsequent degraded performance, including changes in mood, decreased psychomotor vigilance, and an inability to accurately judge one’s own level of impairment (similar to alcohol intoxication).

2. Shortage of sustained nighttime sleep can be supplemented with naps during other times. If other sleep cannot be obtained, stimulants such as caffeine (see our caffeine chewing gum research summary) or prescription medicines such as dextroamphetamine or modafinil can be used to improve alertness and performance until sleep can be obtained. These substances are not substitutes for sleep, just tools to use until adequate sleep can be acquired.

3. Definitely. Naps are particularly helpful prior to night duty and/or extended duty. Also, naps become more beneficial the further the main sleep period is reduced below seven or eight hours. See the preventive strategies and operational countermeasures in HPRC’s research summary on sleep needs.

4. Aside from the preventive strategies and operational countermeasures in HPRC’s research summary, there are some tools available.

The Department of Defense has helped develop a software tool that is used extensively by the USAF and USN to schedule work and rest periods for aviators. The Fatigue Avoidance Scheduling Tool (FAST) is used as an operational risk management tool to schedule sleep and naps and to predict dips in aircrew alertness. USN flight surgeons are trained to use FAST, and it is now used to evaluate all US Naval mishaps.

As for specific advice about sleeping conditions, whether for a major sleep period or for a nap, make sure the environment is conducive to good-quality sleep. Sleep is best in a safe environment. Ideal sleep conditions include a room that is completely dark, cool, and quiet, with a comfortable sleeping surface. Nighttime sleep is easier to initiate and maintain than daytime sleep, which is difficult under most circumstances. A masking noise such as a fan can cover intermittent outside noises. Earplugs are also good for covering outside noises. If a dark room is not available, an eye mask can help screen out light. Sleeping Marines should be housed separately from others; if working shifts, put all night workers in the same tent, room, etc., to keep day workers from disturbing the sleep of night workers and vice versa. Education concerning proper sleep habits also may be helpful for those who have time to sleep but have difficulty going to sleep or staying asleep.

Alertness Management in Military Operations (AMMO) is a program sponsored by the Defense Safety Oversight Council that offers downloadable software allowing leaders to schedule crews optimally by factoring in personnel sleep history, jet lag, and other factors. Also offered to individual Warfighters are Sleep Kits, which come with earplugs, camouflage eye masks, and sleep training tips.

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